Process for optimizing cobalt electrofill using sacrificial oxidants

ABSTRACT

Embodiments herein relate to methods, apparatus, and systems for electroplating metal into recessed features using a superconformal fill mechanism that provides relatively faster plating within a feature and relatively slower plating in the field region. Moreover, within the feature, plating occurs faster toward the bottom of the feature compared to the top of the feature. The result is that the feature is filled with metal from the bottom upwards, resulting in a high quality fill without the formation of seams or voids, defects that are likely where a conformal fill mechanism is used. The superconformal fill mechanism relies on the presence of a sacrificial oxidant molecule that is used to develop a differential current efficiency within the feature compared to the field region. Various plating conditions are balanced against one another to ensure that the feature fills from the bottom upwards. No organic plating additives are necessary, though plating additives can be used to improve the process.

BACKGROUND

In damascene processing, electrodeposition is commonly used to fillrecessed features with cobalt or other metals to fabricate interconnectsand other structures. In order to form high quality interconnects, it isimportant to establish void-free, seam-free fill. In traditionaldamascene processing, organic additives such as suppressor, accelerator,and leveler are used to establish a bottom-up fill mechanism where thefeature is filled from the bottom upwards. The bottom-up fill mechanismforms much higher quality features compared to a conformal fillmechanism, which is likely to form voids and/or seams.

Where a conformal fill mechanism is used, the electrodeposited film isformed at a substantially uniform thickness at all regions of therecessed feature. As the film builds up on the sidewalls of the feature,the sidewalls close in toward one another, forming a seam up the middleof the feature. In many cases, as the sidewalls close in toward oneanother, they pinch off an area near the top of the feature, preventingelectroplating from occurring effectively at positions lower in thefeature. This effect leads to the formation of voids within the feature,which are highly undesirable. As mentioned above, these undesirableeffects are traditionally avoided through the use of organic additivesin the electrolyte that establish a bottom-up fill mechanism, explainedfurther below.

SUMMARY

Certain embodiments herein relate to methods and apparatus forelectroplating metal into a recessed feature on a substrate using asuperconformal fill mechanism. Also described herein are methods foridentifying a set of electroplating conditions that will result in asuperconformal fill mechanism, as well as methods for evaluating whethera set of electroplating conditions will result in a superconformal fillmechanism. The disclosed superconformal fill mechanism relies onestablishing differential current efficiencies at different parts of asubstrate (e.g., within a recessed feature vs. at the field region of afeature, or more specifically, near the bottom of a recessed feature vs.near the top of a recessed feature and the field region). Thedifferential current efficiency results in a greater rate of metaldeposition near the bottom of the feature compared to the top of thefeature, leading to superconformal fill from the bottom of the featureupwards.

In one aspect of the disclosed embodiments, a method of identifying aset of electroplating conditions that will result in a superconformalfill mechanism is provided, the method including: (a) electroplating afirst series of substrates in a first test solution, where a rate ofsubstrate rotation differs between different substrates in the firstseries of substrates, and where a current density differs betweendifferent substrates in the first series of substrates; (b)electroplating a second series of substrates in a second test solution,where the rate of substrate rotation differs between differentsubstrates in the second series of substrates, where the current densitydiffers between different substrates in the second series of substrates,and where the first and second test solutions have differentconcentrations of a sacrificial oxidant; (c) determining a currentefficiency for each substrate in the first and second series ofsubstrates; (d) analyzing the current efficiency and the rate ofsubstrate rotation for each substrate in the first and second series ofsubstrates to identify electroplating conditions, if any, where thecurrent efficiency decreases as the rate of substrate rotation duringdeposition increases; (e) analyzing the current efficiency and theconcentration of sacrificial oxidant for each substrate in the first andsecond series of substrates to identify electroplating conditions, ifany, where the current efficiency decreases as the concentration ofsacrificial oxidant increases; (f) analyzing the current efficiency andthe current density for each substrate in the first and second series ofsubstrates to identify electroplating conditions, if any, where thecurrent efficiency increases as the current density increases; (g) basedon (d)-(f), identifying the set of electroplating conditions that willresult in the superconformal fill mechanism, if any, where the set ofelectroplating conditions that will result in the superconformal fillmechanism include conditions where (i) the current efficiency decreasesas the rate of substrate rotation increases, (ii) the current efficiencydecreases as the concentration of sacrificial oxidant increases, and(iii) the current efficiency increases as the current density increases.

In some embodiments, the first and second test solutions may includecobalt ions, and a metal being deposited on the substrates in the firstand second series of substrates may be cobalt. In a number of suchembodiments, the sacrificial oxidant may be hydrogen ion. In variousimplementations, the sacrificial oxidant, or a material which acts as asource for the sacrificial oxidant, may be selected from the groupconsisting of: a peroxide, dissolved O₂, dissolved O₃, HNO₃, a sugaracid, Cl₂, Br₂, and I₂, and combinations thereof. The reductionpotentials of the sacrificial oxidant and the metal may be balancedagainst one another to ensure superconformal fill. In variousembodiments, a metal being electroplated may reduce at a first reductionpotential, the sacrificial oxidant may reduce at a second potential, andfor the set of electroplating conditions that will result in thesuperconformal fill mechanism, a magnitude of the first reductionpotential may be greater than a magnitude of the second reductionpotential.

The electrolyte may or may not include organic plating additives. Insome embodiments, the first and second test solutions may besubstantially free of suppressor, accelerator, and leveler. In otherembodiments, the first and second test solutions may each includesuppressor.

The concentration of metal ions and sacrificial oxidant may be balancedagainst one another to ensure superconformal fill. In certainembodiments, the first and second test solutions may each include cobaltand hydrogen ions, where a concentration of cobalt ions in the firsttest solution may be at least about 10 times higher than a concentrationof hydrogen ions in the first test solution, and where a concentrationof cobalt ions in the second test solution may be at least about 10times higher than a concentration of hydrogen ions in the second testsolution.

In some implementations, the method may further include electroplatingan additional substrate using electroplating conditions that fall withinthe set of electroplating conditions that will result in thesuperconformal fill mechanism, where the additional substrate includes aplurality of recessed features, and where the recessed features arefilled using the superconformal fill mechanism.

In another aspect of the embodiments herein, a method of electroplatinga recessed feature on a substrate using a superconformal fill mechanismis provided, the method including: (a) immersing the substrate inelectrolyte, the electrolyte including metal ions and a sacrificialoxidant; (b) applying current to the substrate to plate metal in therecessed feature; (c) during (b), depleting a concentration of thesacrificial oxidant within the recessed feature to form a concentrationdifferential with respect to the sacrificial oxidant, where thesacrificial oxidant becomes relatively less abundant within the recessedfeature and relatively more abundant in a field region of the substrate;(d) during (b), developing a current efficiency differential, where thecurrent efficiency is relatively higher within the recessed feature andrelatively lower in the field region of the substrate; and (e) during(b), using the current efficiency differential to drive thesuperconformal fill mechanism that deposits metal relatively faster neara bottom of the recessed feature and relatively slower in the fieldregion of the substrate.

In some such embodiments, during (b), the metal ions are not masstransport limited, such that no substantial concentration differentialforms with respect to the metal ions. In a particular embodiment, themetal ions may be cobalt ions and the sacrificial oxidant may behydrogen ions. In some such embodiments, the electrolyte may includeabout 10-100 mM cobalt ions, about 0.05-0.6 M boric acid, a pH betweenabout 2-4, and a concentration of cobalt ions in the electrolyte may beat least about 10 times higher than a concentration of hydrogen ions inthe electrolyte. In these or other embodiments, during (b) the substratemay be rotated at a rate between about 1-100 RPM, and during (b) currentmay be applied to the substrate at a constant current density of about 4mA/cm² or below. In these or other embodiments, the method may furtherinclude after (a) and before (b), performing a pre-conditioning stepwhere no current or potential is applied to the substrate for a durationbetween about 0.25-30 seconds.

In various embodiments, the sacrificial oxidant, or a material that actsas a source for the sacrificial oxidant, may be selected from the groupconsisting of: a peroxide, dissolved O₂, dissolved O₃, HNO₃, a sugaracid, Cl₂, Br₂, and I₂, and combinations thereof. In someimplementations, the electrolyte may be substantially free ofsuppressor, accelerator, and leveler. In some other implementations, theelectrolyte may further include suppressor. In various embodiments,during (b) a current density applied to the substrate may increase froma starting current density to an ending current density, the startingcurrent density being between about 0-4 mA/cm² and the ending currentdensity being between about 6-10 mA/cm².

In a further aspect of the disclosed embodiments, an apparatus forelectroplating metal into a recessed feature using a superconformal fillmechanism is provided, the apparatus including: an electroplatingchamber configured to hold electrolyte; a substrate holder configured toimmerse the substrate in the electrolyte; and a controller includingexecutable instructions for: (a) immersing the substrate in electrolyte,the electrolyte including metal ions and a sacrificial oxidant; (b)applying current to the substrate to plate metal in the recessedfeature; (c) during (b), depleting a concentration of the sacrificialoxidant within the recessed feature to form a concentration differentialwith respect to the sacrificial oxidant, where the sacrificial oxidantbecomes relatively less abundant within the recessed feature andrelatively more abundant in a field region of the substrate; (d) during(b), developing a current efficiency differential, where the currentefficiency is relatively higher within the recessed feature andrelatively lower in the field region of the substrate; and (e) during(b), using the current efficiency differential to drive thesuperconformal fill mechanism that deposits metal relatively faster neara bottom of the recessed feature and relatively slower in the fieldregion of the substrate.

These and other features will be described below with reference to theassociated drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates a bottom-up fill mechanism.

FIG. 1B illustrates a conformal fill mechanism.

FIG. 2 illustrates a superconformal fill mechanism according to certainembodiments.

FIGS. 3A and 3B present views of an electroplated substrate after achemical mechanical polishing operation.

FIG. 4 provides a flow chart for a method of evaluating whether a set ofelectroplating conditions will lead to a desired superconformal fillmechanism.

FIG. 5 shows experimental results depicting current efficiency over arange of substrate rotation rates, electrolyte pH values, and currentdensities.

FIG. 6 is a graph of reduction current vs. potential, further explainingthe disclosed superconformal fill mechanism.

FIG. 7 is a flow chart for a method of electroplating a substrate with asuperconformal fill mechanism according to certain embodiments.

FIG. 8 illustrates the reductive wave of a cyclic voltammogram in anelectrolyte having cobalt ions and hydrogen ions at variousconcentrations.

FIGS. 9A-9C depict a recessed feature after particular elapsed times aseach feature is filled using the disclosed superconformal fillmechanism.

FIG. 10 shows a simplified view of an electroplating cell according tocertain embodiments.

FIGS. 11 and 12 show simplified views of a multi-station electroplatingapparatus according to certain embodiments.

DETAILED DESCRIPTION

In this application, the terms “semiconductor wafer,” “wafer,”“substrate,” “wafer substrate,” and “partially fabricated integratedcircuit” are used interchangeably. One of ordinary skill in the artwould understand that the term “partially fabricated integrated circuit”can refer to a silicon wafer during any of many stages of integratedcircuit fabrication thereon. A wafer or substrate used in thesemiconductor device industry typically has a diameter of 200 mm, or 300mm, or 450 mm. Further, the terms “electrolyte,” “plating bath,” “bath,”and “plating solution” are used interchangeably. The following detaileddescription assumes the embodiments are implemented on a wafer. However,the embodiments are not so limited. The work piece may be of variousshapes, sizes, and materials. In addition to semiconductor wafers, otherwork pieces that may take advantage of the disclosed embodiments includevarious articles such as printed circuit boards, magnetic recordingmedia, magnetic recording sensors, mirrors, optical elements,micro-mechanical devices and the like.

In the following description, numerous specific details are set forth inorder to provide a thorough understanding of the presented embodiments.The disclosed embodiments may be practiced without some or all of thesespecific details. In other instances, well-known process operations havenot been described in detail to not unnecessarily obscure the disclosedembodiments. While the disclosed embodiments will be described inconjunction with the specific embodiments, it will be understood that itis not intended to limit the disclosed embodiments.

A number of embodiments herein are provided in the context of cobaltdeposition. However, the embodiments are not so limited. Thesuperconformal fill mechanism described herein may also be used to fillfeatures with copper or other metals.

As mentioned above, conventional electrodeposition processes typicallyutilize organic additives such as suppressors, accelerators and levelersto achieve a bottom-up fill. Though the embodiments herein do notrequire the use of these additives, they will be discussed below for thepurpose of explaining the conventional bottom-up fill mechanism. In someembodiments, suppressor and/or accelerator and/or leveler may beprovided in the electrolyte. In other embodiments, these additives maybe omitted.

Suppressors

While not wishing to be bound to any theory or mechanism of action, itis believed that suppressors (either alone or in combination with otherbath additives) are surface-kinetic polarizing compounds that lead to asignificant increase in the voltage drop across thesubstrate-electrolyte interface, especially when present in combinationwith a surface chemisorbing halide (e.g., chloride or bromide). Thehalide may act as a bridge between the suppressor molecules and thewafer surface. The suppressor both (1) increases the local polarizationof the substrate surface at regions where the suppressor is presentrelative to regions where the suppressor is absent, and (2) increasesthe polarization of the substrate surface generally. The increasedpolarization (local and/or general) corresponds to increasedresistivity/impedance and therefore slower plating at a particularapplied potential.

Although suppressors adsorb onto a substrate surface, it is believedthat they are not incorporated into the deposited film and may slowlydegrade over time. Compounds which do not principally act by adsorbingonto a substrate surface are not considered suppressors. Suppressors areoften relatively large molecules, and in many instances they arepolymeric in nature (e.g., polyethylene oxide, polypropylene oxide,polyethylene glycol, polypropylene glycol, etc.). Other examples ofsuppressors include polyethylene and polypropylene oxides with S- and/orN-containing functional groups, block polymers of polyethylene oxide andpolypropylene oxides, etc. The suppressors can have linear chainstructures or branch structures. It is common that suppressor moleculeswith various molecular weights co-exist in a commercial suppressorsolution. Due in part to suppressors' large size, the diffusion of thesecompounds into a recessed feature is relatively slow.

Accelerators

While not wishing to be bound by any theory or mechanism of action, itis believed that accelerators (either alone or in combination with otherbath additives) tend to locally reduce the polarization effectassociated with the presence of suppressors, and thereby locallyincrease the electrodeposition rate. The reduced polarization effect ismost pronounced in regions where the adsorbed accelerator is mostconcentrated (i.e., the polarization is reduced as a function of thelocal surface concentration of adsorbed accelerator). Exampleaccelerators include, but are not limited to, dimercaptopropane sulfonicacid, dimercaptoethane sulfonic acid, mercaptopropane sulfonic acid,mercaptoethane sulfonic acid, bis-(3-sulfopropyl) disulfide (SPS), andtheir derivatives. Although the accelerator may become strongly adsorbedto the substrate surface and generally laterally-surface immobile as aresult of the plating reactions, the accelerator is generally notincorporated into the film. Thus, the accelerator remains on the surfaceas metal is deposited. As a recess is filled, the local acceleratorconcentration increases on the surface within the recess. Acceleratorstend to be smaller molecules and exhibit faster diffusion into recessedfeatures, as compared to suppressors. Compounds which do not principallyact by adsorbing onto a substrate surface are not considered to beaccelerators.

Levelers

While not wishing to be bound by any theory or mechanism of action, itis believed that levelers (either alone or in combination with otherbath additives) act as suppressing agents to counteract thedepolarization effect associated with accelerators, especially in thefield region and at the side walls of a feature. The leveler may locallyincrease the polarization/surface resistance of the substrate, therebyslowing the local electrodeposition reaction in regions where theleveler is adsorbed. The local concentration of levelers is determinedto some degree by mass transport. Therefore, levelers act principally onsurface structures having geometries that protrude away from thesurface. This action “smooths” the surface of the electrodepositedlayer. It is believed that leveler reacts or is consumed at thesubstrate surface at a rate that is at or near a diffusion limited rate,and therefore, a continuous supply of leveler is often beneficial inmaintaining uniform plating conditions over time.

Leveler compounds are generally classified as levelers based on theirelectrochemical function and impact and do not require specific chemicalstructure or formulation. However, levelers often contain one or morenitrogen, amine, imide or imidazole, and may also contain sulfurfunctional groups. Compounds which do not principally act by adsorbingonto a substrate surface are not considered levelers. Certain levelersinclude one or more five and six member rings and/or conjugated organiccompound derivatives. Nitrogen groups may form part of the ringstructure. In amine-containing levelers, the amines may be primary,secondary or tertiary alkyl amines. Furthermore, the amine may be anaryl amine or a heterocyclic amine. Example amines include, but are notlimited to, dialkylamines, trialkylamines, arylalkylamines, triazoles,imidazole, triazole, tetrazole, benzimidazole, benzotriazole,piperidine, morpholines, piperazine, pyridine, oxazole, benzoxazole,pyrimidine, quonoline, and isoquinoline. Imidazole and pyridine may beespecially useful. Leveler compounds may also include ethoxide groups.For example, the leveler may include a general backbone similar to thatfound in polyethylene glycol or polyethyelene oxide, with fragments ofamine functionally inserted over the chain (e.g., Janus Green B).Example epoxides include, but are not limited to, epihalohydrins such asepichlorohydrin and epibromohydrin, and polyepoxide compounds.Polyepoxide compounds having two or more epoxide moieties joinedtogether by an ether-containing linkage may be especially useful. Someleveler compounds are polymeric, while others are not. Example polymericleveler compounds include, but are not limited to, polyethylenimine,polyamidoamines, and reaction products of an amine with various oxygenepoxides or sulfides. One example of a non-polymeric leveler is6-mercapto-hexanol. Another example leveler is polyvinylpyrrolidone(PVP).

Bottom-Up Fill Promoted by Organic Additives

In a bottom-up fill mechanism, illustrated in FIG. 1A, a recessedfeature on a plating surface tends to be plated with metal from thebottom to the top of the feature, and to a lesser degree, inward fromthe side walls towards the center of the feature. It is important tocontrol the deposition rate within the feature and in the field regionin order to achieve uniform filling and avoid incorporating voids intothe features. In conventional applications, the three types of additivesdescribed above are necessary in accomplishing bottom-up fill, eachworking to selectively increase or decrease the polarization atparticular regions on the substrate surface.

After the substrate is immersed in electrolyte, the suppressor adsorbsonto the surface of the substrate, especially in exposed regions such asthe field region. At the initial plating stages, there is a substantialdifferential in suppressor concentration between the top and bottom of arecessed feature. This differential is present due to the relativelylarge size of the suppressor molecule and its correspondingly slowtransport properties. Over this same initial plating time, it isbelieved that accelerator accumulates at a low, substantially uniformconcentration over the entire plating surface, including the bottom andside walls of the feature. Because the accelerator diffuses intofeatures more rapidly than the suppressor, the initial ratio ofaccelerator:suppressor within the feature (especially at the featurebottom) is relatively high. The relatively high initialaccelerator:suppressor ratio within the feature (especially at thefeature bottom) promotes rapid plating near the bottom of the featurecompared to the top of the feature. Meanwhile, the initial plating ratein the field region and toward the top of the feature is relatively lowdue to the lower ratio of accelerator:suppressor. Thus, in the initialplating stages, plating occurs relatively faster within the feature,particularly near the feature bottom, and relatively slower in the fieldregion and toward the top of the feature.

As plating continues, the feature fills with metal and the surface areawithin the feature is reduced, as shown in FIG. 1A. Because of thedecreasing surface area and the accelerator substantially remaining onthe surface, the local surface concentration of accelerator within thefeature (especially at the feature bottom) increases as platingcontinues. This increased accelerator concentration near the featurebottom helps maintain the differential plating rate needed for bottom-upfill.

In the later stages of plating, particularly as overburden deposits, theaccelerator may build up in certain regions (e.g., above filledfeatures) undesirably, resulting in local faster-than-desired plating.Leveler is conventionally used to counteract this effect. The surfaceconcentration of leveler is greatest at exposed regions of a surface(i.e., not within recessed features) and where convection is greatest.It is believed that the leveler displaces accelerator, increases thelocal polarization and decreases the local plating rate at regions ofthe surface that would otherwise be plating at a rate greater than atother locations on the deposit. In other words, the leveler tends, atleast in part, to reduce or remove the influence of an acceleratingcompound at the exposed regions of a surface, particularly at protrudingstructures. In conventional applications, a feature may tend to overfilland produce a bump in the absence of leveler. Therefore, in the laterstages of conventional bottom-up fill plating, levelers are beneficialin producing a relatively flat deposit.

The use of suppressor, accelerator and leveler, in combination, havetraditionally allowed a feature to be filled without voids from thebottom-up, while producing a relatively flat deposited surface. Theexact identity/composition of the additive compounds are typicallymaintained as trade secrets by the additive suppliers, thus, informationabout the exact nature of these compounds is not publicly available.

One problem with additive-based bottom-up fill is that it is difficultto practice where very small feature sizes are used. This may be becauseit is difficult or impossible to diffuse the additives into the featuresas needed when the features are sufficiently small, e.g., due to thesize of the additives compared to the feature size, and/or due to theshort timeframes for filling such small volumes. For example, in variouscases where the features are very small, the features may fill morequickly than the timeframe needed for the additives to diffuse into thefeatures and establish differential plating rates, as described above.In many cases, additive-based bottom-up fill is only effective atfeature sizes (widths) of about 20 nm or greater. In a number ofembodiments herein, feature sizes may be about 30 nm or less, forexample about 20 nm or less, or about 15 nm or less, or about 10 nm orless. Because the embodiments herein do not rely on the describedadditives, they can be practiced even at extremely small feature sizes,e.g., down to about 2 or 3 nm.

Another problem associated with additive-based bottom-up fill is theincorporation of impurities into the electrodeposited film. Becauseadditive-based bottom-up fill relies on direct interactions between theorganic additive molecules and the plated metal surface, these processesare prone to incorporation of elements from the additives into thedeposited film. Such impurities are further discussed below in thecontext of FIGS. 3A and 3B.

Conformal Fill

The bottom-up fill mechanism described above in relation to FIG. 1A canbe contrasted with the conformal fill mechanism shown in FIG. 1B. Asshown in FIG. 1B, where conformal plating is used, the film plates at arelatively uniform thickness on all of the surfaces, including both thebottom and the sidewalls of the feature. While conformal plating can beused to fill features, it typically results in a seam up the middle ofthe feature where the two sidewalls meet. Moreover, in many casesconformal plating can lead to the formation of voids within features.Such voids can be formed as the sidewalls of the feature approach oneanother and pinch off a region toward the top of the feature. Thispinching off prevents electroplating from occurring at positions thatare lower in the feature, resulting in the formation of a void, ratherthan a tight seam. Electrolyte can become trapped in these voids. Bothseams and voids are undesirable in a filled feature.

Superconformal Fill Promoted by Sacrificial Oxidants

A superconformal fill mechanism is one in which film deposits relativelyfaster near the bottom of a recessed feature and relatively slower nearthe top of the feature. Bottom-up fill is one kind of superconformalfill mechanism. In bottom-up fill, the bottom of a partially filledfeature may remain relatively flat throughout much of the fill process,as shown in FIG. 1A. As used herein, superconformal fill also includescases where the deposited film forms in a V-shape within a partiallyfilled feature throughout much of the fill process, as shown in FIG. 2.

Conventionally, it was believed that the plating additives describedabove were necessary to establish superconformal fill within a recessedfeature. However, in the embodiments herein, an alternativesuperconformal fill process is provided that does not rely on suchplating additives. Although such additives may be used in someimplementations, they are not needed to establish superconformal fill.Instead, superconformal fill is accomplished by balancing severalplating conditions to ensure differential plating rates within thefeature. In this way, a relatively high plating rate can be establishedat the bottom of the feature compared to the top of the feature, leadingto high quality superconformal fill and avoiding the formation of seamsand voids.

The differential plating rate may be established by providing asacrificial oxidant that is more abundant and/or active on the fieldregion and near the top of the feature compared to the bottom of thefeature. As used herein, the term sacrificial oxidant refers to asolution in the electrolyte that is reduced at the electrode (e.g.,substrate) surface instead of the metal ion of interest.

The sacrificial oxidant effectively diverts current that would otherwisebe used to reduce/deposit metal. Because the plating conditions (e.g.,electrolyte composition, applied current and/or potential, andconvection conditions (e.g., rotation rate of the substrate)) aretailored to ensure that the sacrificial oxidant is more active and/orabundant on the field region and near the top of the feature compared tothe bottom of the feature, and because the sacrificial oxidant affectsthe local current efficiency (e.g., the fraction of current that goestoward reducing metal), a differential current efficiency is establishedwithin the feature. In other words, near the top of the feature wherethe sacrificial oxidant is relatively more abundant or active, arelatively greater proportion of the deposition current is diverted toreducing the sacrificial oxidant, and relatively less metal isdeposited. By contrast, near the bottom of the feature where thesacrificial oxidant is relatively less abundant or active, a relativelylower proportion of the deposition current is diverted to reducing thesacrificial oxidant, and relatively more metal is deposited.

The result is that differential metal plating rates are established atdifferent parts of the feature, with metal plating occurring faster nearthe bottom of the feature and slower near the top of the feature and inthe field region. Similarly, differential sacrificial oxidant reductionrates are established at different parts of the feature, withsacrificial oxidant reduction occurring at a greater rate near the topof the feature, and at a lower rate near the bottom of the feature. Thedifferential current efficiency at different regions of the featureresults in superconformal fill, without any need to rely on organicadditives such as suppressor, accelerator, and leveler.

This fill mechanism is illustrated in FIG. 2, which is described in thecontext of cobalt deposition. The cobalt ions are shown as dark circles,while the sacrificial oxidant molecules are shown as light circles.Toward the beginning of the deposition process, both cobalt ions andsacrificial oxidant molecules diffuse into the feature. Because of theinitial abundance of sacrificial oxidant molecules, there is arelatively low current efficiency (CE) at both the bottom and top of thefeature.

After a short period of time, the sacrificial oxidant molecules becomedepleted near the feature bottom, and a relatively higher currentefficiency is established near the bottom of the feature compared to thetop of the feature. The sacrificial oxidant depletes more substantiallywithin the feature compared to the field region due to the relativelyhigher surface area to volume ratio within the feature. The sacrificialoxidant molecules continue to diffuse into the feature to some degree,and due to the balance of plating conditions and feature shape, thesacrificial oxidant molecules become more abundant (and/or active) nearthe top of the feature compared to the bottom of the feature. Thisdifferential abundance and/or activity of the sacrificial oxidantmolecules arises at least partly because these molecules have to diffusefrom the bulk solution down toward the feature bottom, and becausesacrificial oxidant molecules are chosen such that they require lessenergy to reduce than the metal being deposited.

As the deposition process continues, the relatively high currentefficiency near the bottom of the feature compared to the top of thefeature results in a greater degree of cobalt deposition near the bottomof the feature compared to the top of the feature. This trend continuesas the feature is filled from the bottom upwards.

In most conventional electroplating approaches, one of the goals is tomaximize current efficiency. Current efficiency can be defined asfollows:

$\begin{matrix}{{{Current}\mspace{14mu} {Efficiency}} = \frac{I_{M}}{I_{T}}} & {{Equation}\mspace{14mu} 1}\end{matrix}$

where,I_(M)=the current that acts to deposit metal, andI_(T)=the total current applied to the substrate

I_(T) can be measured directly based on the number of coulombs appliedto the substrate over time during processing. I_(M) can be calculatedbased on the amount (e.g., thickness) of metal deposited on thesubstrate over time during processing.

Current efficiency can be considered both as an overall value reflectingthe entire electroplating process/feature, and as a local valuereflecting a particular portion of the substrate/feature. It isgenerally desirable to maximize current efficiency in order to minimizethe amount of wasted current/power during processing. In conventionalcases, the “wasted” current (current that is applied to the substratebut not used to deposit metal) can be calculated as follows:

Wasted Current=I _(T) −I _(M)  Equation 2:

In conventional approaches, electroplating processes are optimized tominimize the wasted current (such that I_(M) is very close to I_(T)),thereby maximizing the current efficiency toward 1. This approachminimizes processing costs associated with power delivery. Further, thisapproach minimizes processing time (e.g., because a high proportion ofcurrent is used to deposit metal, it takes relatively less time to filla feature). Another reason that conventional electroplating approachesoptimize for high current efficiency is to maintain a stable electrolytecomposition. In cases where current efficiency is low and a relativelyhigh proportion of current is diverted to reducing other species in theelectrolyte, the concentration of such species can change over time,which is typically undesirable for establishing uniform processingconditions and electroplating results.

The embodiments herein use a different approach, specifically optimizingfor a low current efficiency near the top of the recessed feature and inthe field region. This approach is quite different from conventionaltechniques, as the current efficiency is being optimized in asubstantially different way, and for different reasons.

The disclosed superconformal plating mechanism provides a number ofadvantages over traditional approaches that rely on organic platingadditives. For example, the disclosed mechanism scales very well withfeature size, and can be used to fill smaller features compared toadditive-based processes. Additive-based processes are typicallyunsuccessful below a particular feature size, for example because theadditives (e.g., large suppressor molecules, etc.) may not be able todiffuse into the features as needed to establish differential platingrates. This may be because the additives are too large to fit into thefeatures, and/or because the features fill too quickly (e.g., due to lowvolume) for the additives to diffuse into and adsorb onto the feature toestablish the required concentrations, where needed. By contrast, withthe disclosed superconformal mechanism, smaller features may benefiteven more greatly (e.g., fill may be superconformal to a greater degree)than relatively larger features, e.g., due to the relatively highersurface area to volume ratio in the smaller features. The high surfacearea to volume ratio promotes depletion of the sacrificial oxidantmolecules, which drives the differential plating rates and the resultingsuperconformal fill. Further, because the disclosed mechanism relies ondiffusion of small molecules (the sacrificial oxidant molecules) insidethe feature (e.g., as opposed to large suppressor molecules or otherlarge additive molecules), the inability of large macromolecularadditive molecules does not deleteriously affect the fill behavior.

Moreover, because the disclosed superconformal fill mechanism does notrely on direct adsorption of organic additive molecules, the likelihoodof incorporating unwanted contaminants into the film is minimized. Onereason to avoid such contaminants is that they undesirably increase theroughness and resistivity of the deposited film. Low resistivity isimportant for producing high quality connections in semiconductordevices. Another reason to avoid such contaminants is that the slurriesused for chemical-mechanical polishing (CMP) processes (which typicallyoccur after the features are filled) are sensitive to even small amountsof impurities in the film. This is particularly true for sulfurimpurities, which can produce significant corrosion during theplanarization process.

FIGS. 3A and 3B illustrate a comparison between post-CMP results for acobalt film that includes sulfur impurities (FIG. 3A) and a cobalt filmwith a negligible sulfur content (FIG. 3B). The film in FIG. 3A showsunacceptable CMP results, illustrating a rough surface as shown by thehigh contrast between different areas of the film. The dark contrast onthe lines indicates the presence of large voids in the film. The film inFIG. 3B shows acceptable CMP results, illustrating a film that issubstantially less rough and higher quality.

Although the disclosed superconformal fill mechanism is attractive intheory, in practice it can be quite difficult to adequately balance allof the relevant process conditions to ensure that the requireddifferential current efficiency is established (e.g., at differentportions of the feature, and within the feature compared to the fieldregion). Specific parameters which are balanced against one anotherinclude: (a) the ratio of metal ion to sacrificial oxidant molecule, (b)the concentration of metal ion, (c) the concentration of sacrificialoxidant molecule, (d) the degree of convective mass transport (which maybe affected by the rotation rate of the substrate, for example), (e)temperature of the electrolyte, and (f) the relative and absolutereduction potentials of the metal ions and sacrificial oxidant molecules(which may be affected by complexation or lack thereof, concentration ofthe relevant species, the material of the substrate, the choice(composition) of the metal ion, and the choice (composition) of thesacrificial oxidant molecule).

Also disclosed herein are methods for designing an electroplatingprocess to take advantage of the disclosed superconformal fillmechanism. Such methods are described in the context of FIGS. 4-6.

FIG. 4 is a flowchart describing a method of designing/testing anelectroplating process to achieve superconformal fill. The method beginsat operation 401, where a series of substrates are electroplated in atleast a first test solution and a second test solution, over a range ofdifferent substrate rotation rates, and over a range of differentcurrent densities. The first test solution and the second test solution(and additional test solutions, if provided) may have the samecomposition except for having differing concentrations of sacrificialoxidant molecules. In various embodiments where the sacrificial oxidantis H⁺, the two test solutions may have the same composition except forhaving differing pH values.

In operation 403, the current efficiency is measured for eachelectroplated substrate. Example results are plotted in FIG. 5. In thecontext of FIG. 5, two different test solutions were tested, a firsttest solution having a pH of about 3 and a second test solution having apH of about 4. Three different substrate rotation rates (about 12 RPM,about 50 RPM, and about 100 RPM) were tested, and three differentconstant current densities (about 1 mA/cm², about 2 mA/cm², and about 8mA/cm²) were tested. The resulting current efficiencies for each exampleare shown in FIG. 5.

In operation 405, it is determined whether the current efficiencydecreases as the substrate rotation rate increases. For the exampleshown in FIG. 5, it can be seen that for each given test solution andcurrent density, current efficiency is lower at the higher substraterotation rates. In other words, as the rate of substrate rotationincreases, the current efficiency decreases. This relationship indicatesthat over the tested plating conditions, the sacrificial oxidant is masstransport limited, a condition that is needed for the disclosedsuperconformal fill mechanism to be successful. Larger differences incurrent efficiency indicate better superconformal fill conditions, asthis difference indicates that the current efficiency is relatively moresensitive to mass transport control of the sacrificial oxidant species.

In cases where the current efficiency decreases as the substraterotation rate increases, the method continues at operation 406, where itis determined whether the current efficiency decreases as theconcentration of the sacrificial oxidant increases. A negativecorrelation between current efficiency and the concentration ofsacrificial oxidant indicates that the decrease in current efficiency isrelated to increased competition between reduction of the metal ions andreduction of the sacrificial oxidant molecules. In other words, thisrelationship provides an indication of whether the different reductionreactions are properly balanced against one another. In cases where thesacrificial oxidant is H⁺, operation 406 involves determining whetherthe current efficiency decreases as the pH of the test solutionsdecrease.

In the context of FIG. 5, the current efficiency decreases as the pH ofthe test solutions decrease (e.g., as the concentration of sacrificialH⁺ in the test solutions increase), at least for certain tested currentdensities. The decrease in current efficiency with lower pH was true atall tested substrate rotation rates in cases where the current densityduring plating was 1 mA/cm² or 2 mA/cm². Where the current density was 8mA/cm² during plating, the difference in pH had no substantial effect onthe current efficiency. This may indicate that for the conditionstested, superconformal fill is likely to occur at the lower currentdensities, e.g., 1 and 2 mA/cm², but likely will not be successful (oras successful) at current densities as high as 8 mA/cm². Additionalcurrent densities, pH values, and substrate rotation rates may be testedin order to determine the limits of the conditions likely to lead tosuperconformal fill, if desired.

In cases where the current efficiency decreases as the concentration ofsacrificial oxidant increases, the method continues with operation 407,where it is determined whether the current efficiency increases as thecurrent density increases. A positive correlation between the currentefficiency and the current density indicates that the reductivepotential and concentration of the sacrificial oxidant are properlytuned. In the context of FIG. 5, for a given substrate rotation rate andpH, higher current densities show higher current efficiencies,indicating that the reductive potential and sacrificial oxidantconcentrations tested are likely to lead to the desired superconformalfill.

In cases where a set of conditions is identified where (a) the currentefficiency decreases as the substrate rotation rate increases (e.g.,operation 405=yes), (b) the current efficiency decreases and theconcentration of sacrificial oxidant increases (e.g., operation406=yes), and (c) the current efficiency increases as the currentdensity increase (e.g., operation 407=yes), the method continues withoperation 409, where it is determined that the identified set ofconditions is likely to produce the desired superconformal fillmechanism that relies on establishing different current efficiencies atdifferent parts of a feature/substrate. The listed current efficiencytrends need not hold true over the entire range of tested conditions. Infact, identifying cases where the trends break down may indicate thelimits of the conditions likely to lead to superconformal fill. In theexample of FIG. 5, because the current efficiency is essentiallyunaffected by the change in pH (i.e., the change in the concentration ofthe sacrificial oxidant molecule) when the current density was 8 mA/cm²,this may indicate that the current density should be kept below about 8mA/cm² to produce superconformal fill. As mentioned, additional testingcan be pursued to more accurately characterize the outer limits of theacceptable processing window.

The method may optionally continue with operation 411, where a substratemay be electroplated using a set of conditions identified in operations401-409 to be likely to produce superconformal fill.

In cases where either (a) the current efficiency does not decrease asthe substrate rotation rate increases (e.g., operation 405=no), (b) thecurrent efficiency does not decrease as the concentration of sacrificialoxidant increases (e.g., operation 406=no), or (c) the currentefficiency does not increase as the current density increases (e.g.,operation 407=no), the method continues with operation 413, where it isdetermined that the electroplating conditions tested are not likely toproduce superconformal fill. In various embodiments, the method may thencontinue with operation 415, where the electroplating conditions arealtered. This may involve, e.g., (i) changing the concentration ofsacrificial oxidant molecules, (ii) changing the concentration of metalions, (iii) changing the rotation rate of substrate during deposition,(iv) changing the temperature of electrolyte and/or substrate, (v)changing the complexation (if any) of the metal ion, (vi) changing thecomplexation (if any) of the sacrificial oxidant molecule, (vii)changing the identity/composition of sacrificial oxidant molecule,(viii) changing the current density during deposition, (ix) changing thecomposition of the test solutions to adjust a concentration of one ormore organic additives (e.g., suppressor), which may or may not bepresent.

FIG. 6 provides a schematic of the electrochemical interaction between ametal reduction reaction and a sacrificial oxidant reduction reaction inan electroplating system where a sacrificial oxidant is provided toestablish differential current efficiencies at different portions of thefeature/substrate. This figure can be used to further explain thedisclosed superconformal fill mechanism and the considerations that gointo designing an electroplating process to take advantage of thismechanism. The traces in FIG. 6 depict the expected reduction currentobserved during the application of a ramping potential applied to thesubstrate. In each trace, the reduction current starts at zero, thenbegins to increase close to the relevant reduction potential. At valueswell above the reduction potential, the reactions are mass transportlimited, and the reduction current levels off.

Traces 1, 2, and 3 illustrate the traces related to reduction ofsacrificial oxidant molecules, with the three different traces relatingto three different concentrations of sacrificial oxidant molecules.Trace 1 relates to the highest concentration of sacrificial oxidantmolecules, while trace 3 relates to the lowest concentration ofsacrificial oxidant molecules. In cases where the sacrificial oxidantmolecule is H⁺, trace 1 relates to the lowest pH, and trace 3 relates tothe highest pH. As expected, trace 1 shows the highest level ofreduction current at a given potential within the mass-transport-limitedregime (e.g., where traces 1-3 are fairly flat/horizontal), indicatingthat more reduction current is used to reduce the sacrificial oxidantmolecules where such molecules are relatively more abundant.

Traces A, B, and C illustrate the traces related to reduction of metalions. These traces relate to a constant metal ion concentration, butthree different reduction potentials. The reduction potentials can beadjusted higher by using a complexing agent that acts to (a) stabilizethe metal ions (e.g., Co²⁺) in solution and/or (b) obscure an activedeposition site on the substrate. The reduction potentials can beadjusted lower by using a complexing agent that acts to (a) stabilize areaction intermediate (e.g., Co⁺) in solution and/or (b) creates acatalytic site on the substrate. Temperature of the electrolyte and/orsubstrate may also affect traces 1-3 and A-C.

In traditional damascene electroplating approaches, it is preferable toensure that reduction of the metal ions is not affected by otherreduction reactions that may take place. In other words, it ispreferable to ensure that the metal ions are reduced at a potential thatis sufficiently below the potential at which any other oxidants arereduced. In the context of FIG. 6, traditional damascene processes wouldprefer to operate at trace A. Because the potential at which metal isreduced in trace A is significantly below the reduction potential atwhich the sacrificial oxidant (if present) is reduced (e.g., in FIG. 5the reduction potential at which trace A deposits metal is significantlybelow the reduction potential at which the sacrificial oxidant isreduced, for all concentrations of the sacrificial oxidant shown), thereaction can proceed at a high degree of current efficiency, with littleor no current being diverted to reduce the sacrificial oxidant. Thisresult is desirable in conventional damascene methods for the reasonsdescribed above.

By contrast, where the disclosed superconformal fill mechanism isdesired, it is important to ensure that both the metal reductionreaction and the sacrificial oxidant reduction reaction occur at similarreduction potentials, such that these reactions can compete with oneanother during deposition. Further, it is desirable to ensure that thepotential at which metal is reduced is one that achieves differentlevels of sacrificial oxidant reduction, depending on the concentrationof the sacrificial oxidant. This ensures that if and when aconcentration gradient of the sacrificial oxidant develops within thefeature (e.g., with the sacrificial oxidant being more abundant in thefield region and near the top of the feature, and more scarce near thebottom of the feature), this concentration gradient leads to differinglevels of current being diverted to reducing the sacrificial oxidant,thereby leading to differential current efficiencies at differentportions of the feature/substrate. The conditions leading to trace Awould not result in the disclosed superconformal fill mechanism at leastbecause there would be no substantial competition between metalreduction and sacrificial oxidant reduction within the feature. Instead,substantially all of the total reduction current would be used to reducemetal, and a conformal fill mechanism is likely to result (at least incases where no organic additives are used).

In one example, the metal reduction reaction is Co²⁺+2e⁻→Co, and thesacrificial oxidant reduction reaction is 2H⁺+2e⁻→H₂. The cobalt isprovided at a concentration such that the cobalt reduction reactionproceeds according to trace B. The electrolyte has a bulk pH of about 3.Trace 1 relates to the hydrogen reduction reaction at pH 3, trace 2relates to the hydrogen reduction reaction at a higher pH, e.g., about3.5, and trace 3 relates to the hydrogen reduction reaction at thehighest pH, e.g., about 4. The reduction potential used duringdeposition is a. The plating conditions are chosen to ensure that duringplating, a hydrogen ion concentration gradient develops within thefeature. This concentration gradient develops at least in part as aresult of the high surface area to volume ratio within the feature. Thehigh surface area to volume ratio promotes rapid depletion of thehydrogen ions within the feature. The plating conditions may be chosenaccording to the method described in relation to FIG. 4, for example.

The resulting hydrogen ion concentration gradient within the featuremeans that the hydrogen reduction reaction will occur at differentdegrees at different portions of the feature. For example, where thehydrogen ions are most concentrated (e.g., in the bulk solution or nearthe top of the feature/field region where pH is about 3, represented bytrace 1), the hydrogen reduction reaction occurs to the greatest degree.This is indicated by the fact that trace 1 has the highest reductioncurrent at a given potential. Similarly, where the hydrogen ions areleast concentrated (e.g., near the bottom of the feature where the H⁺ isdepleted and the pH is closer to about 4, represented by trace 3), thehydrogen reduction reaction occurs to the lowest degree. This isindicated by the fact that trace 3 has the lowest reduction current at agiven potential. The result is that near the top of the feature, much ofthe reduction current is diverted to reducing the hydrogen ions, and thecurrent efficiency in this region is low. This means that relativelyless cobalt is being deposited near the top of the feature. Likewise,near the bottom of the feature, very little of the reduction current isdiverted to reducing the hydrogen ions, and the current efficiency inthis region is relatively high. This means that relatively more cobaltis deposited near the bottom of the feature. The resulting fillmechanism is superconformal, with the feature being filled from thebottom upwards.

In certain embodiments where the metal reduction reaction occursaccording to trace A or C, a suppressor may be provided to the platingsolution to shift the metal reduction reaction so that it more closelyresembles trace B (in terms of overlapping with traces 1-3). Moreover,because of the diffusion considerations involved, the suppressor maypreferentially act to shift the metal reduction potential more in thefield region (where the suppressor is more abundant) than within thefeature (where the suppressor is relatively less abundant). In thiscase, metal deposition on the field region may proceed closer to traceC, while within the feature the metal deposition proceeds closer totrace A. This can result in a very large difference in currentefficiency between the bottom of the feature and the field region.

The combination of shifting the deposition potential through use of asuppressor, along with sacrificial oxidant depletion, is quite powerfulin terms of achieving different current efficiencies and metaldeposition rates at different portions of a feature/substrate. Forinstance, if the region within the feature (e.g., near the bottom of thefeature) is not experiencing a potential shift due to lack of suppressorwithin the feature (trace B), and the concentration of sacrificialoxidant within the feature is depleted (trace 3), then the currentefficiency near the bottom of the feature will be quite high. In thissame example, if the field region of the feature experiences asuppressive potential shift due to the presence of suppressor in thefield region (trace C) and the concentration of sacrificial oxidant isrelatively high in the field region where it is not depleted (trace 1),then the current efficiency in the field region will be quite low. Thedifference in current efficiency at different regions of thefeature/substrate leads to the desired superconformal fill.

In certain embodiments, organic plating additives such as suppressor,accelerator, and leveler may be omitted from the electrolyte. In otherembodiments, one or more of these additives may be provided. Theadditives may act to enhance the superconformal fill mechanism, asdescribed. The additives (e.g., suppressor, in some cases) may providepolarization differences typical of traditional damascene fillchemistries, enhancing the superconformal nature of the fill mechanismby interfering with metal deposition to a greater degree on the fieldregion compared to within the feature. Moreover, the additives mayaffect the activity of the sacrificial oxidant molecules. In someimplementations, the additives may interfere with the reduction of thesacrificial oxidant molecules in the feature to a greater extent than inthe field region. This would further promote a greater degree of metalplating within the feature compared to the field region. Further, theadditives may act to modulate the relative reduction potentials of themetal ions and the sacrificial oxidant molecules, for example throughcomplexation in solution and/or through modification of the surface ofthe substrate. The identity and concentration of any such additives canbe tailored to correctly distribute the additive activity between thefield region and within the feature.

Unexpectedly, an electroplating process that is well optimized to takeadvantage of the disclosed superconformal fill mechanism is expected tohave a lower overall current efficiency compared to even poorlyoptimized conventional electroplating processes (which typically aredesigned for high current efficiency). It was not previously known orexpected that low current efficiency processes were in any waybeneficial for superconformal fill. Indeed, low current efficiencyapproaches have been avoided in practice.

FIG. 7 illustrates a flowchart for a method of electroplating metal ontoa substrate to achieve superconformal fill according to certainembodiments. The method begins at operation 701, where a substrate isimmersed in electrolyte. The substrate may be immersed at an angle toavoid trapping bubbles under its surface. The substrate may be rotatedduring immersion.

At operation 703, an optional pre-conditioning step may be performed.The pre-conditioning step involves a short time period (e.g., 0-30seconds, in some cases at least about 0.25 seconds, at least about 0.5seconds, at least about 1 second, at least about 5 seconds, or at leastabout 10 seconds) after immersion, with no reductive current beingpassed to the substrate. Metals that are exposed to atmosphere gain acoating of native oxide on their surface. Metals with more cathodicreduction potentials (which are generally better suited to theapplication of the disclosed superconformal fill mechanism that relieson differential current efficiencies) are particularly susceptible toformation of such oxides. This native oxide can interfere withnucleation during electroplating. By providing a short time period afterimmersion where no reductive current is passed to the substrate, thisnative oxide can be removed by the corrosive activity of theelectrolyte.

At operation 705, current is applied to the substrate to cause metal tobe plated in the features. The various plating conditions are balancedagainst one another as described herein to ensure that a differentialcurrent efficiency develops between the field region and within thefeature, as discussed further in relation to operations 707-710, below.For example, the current efficiency is relatively high within thefeature, particularly near the bottom of the feature, and is relativelylow in the field region and near the top of the feature.

In some embodiments, a constant current density is provided while metalis plated in the features. In certain implementations, a constantcurrent density of about 4 mA/cm² or lower may be used. The constantcurrent density may be at least about 0.5 mA/cm², or at least about 1mA/cm² in various embodiments. Current densities at this level have beenshown, when properly balanced against other plating conditions, toresult in the desired superconformal fill mechanism.

In some other embodiments, the current density may be ramped up as thefeatures are filled with metal. In one example, the current density maystart at a value between about 0-4 mA/cm², for example between about 0-2mA/cm², and ramp up to a value between about 6-10 mA/cm², for examplebetween about 8-10 mA/cm². The disclosed mechanism relies, to somedegree, on the metal species being less mass transport limited than thesacrificial oxidant, such that the sacrificial oxidant becomes depletedwithin the feature, but the metal remains readily available both in thefield region and within the feature. The described mechanism is mosteffective at relatively low current densities which are sufficientlyhigh to cause depletion of the sacrificial oxidant within the feature,while not being sufficiently high to cause similar depletion of themetal ion within the feature. However, at very low current densities,the seed layer on the field region can become damaged due toinsufficient electrode polarization, causing dissolution of the seedlayer. Additionally, at low current densities, small differences inoverpotential across a part can cause large differences in plating ratesdue to how close the potential is to the deposition potential of themetal. This leads to poor uniformity in plating results. Better qualityplating can be achieved by changing the applied current from a lowervalue to a higher value over the course of electroplating. The rampingcurrent addresses the field region seed dissolution problem by onlyholding at very low current densities for a short time at the beginningof the fill, when the unfilled area of the feature is at a maximum. Theramping current addresses the uniformity problem by ensuring that allareas of the feature/substrate experience a similar potential increase(even if this occurs at differing times), thereby improving the finaluniformity of the plated film. Current waveforms can be ramped uplinearly, stepwise, or as a function mirroring the estimated decrease inthe unplated volume within the feature.

Regardless of the current waveform used while the features are platedwith metal, operation 705 may further involve application of current tothe substrate to deposit overburden on the field region. The currentdensity used during deposition of the overburden may be higher than thecurrent density applied while the features are filled.

Operations 707-710 describe the superconformal fill mechanism. Theseoperations occur during plating, e.g., during operation 705. Inoperation 707, the concentration of the sacrificial oxidant is depletedwithin the recessed features. This forms a concentration differential(in various embodiments a concentration gradient) with respect to thesacrificial oxidant, with the sacrificial oxidant being relatively moreabundant in the field region and near the top of the feature, andrelatively less abundant within the feature, particularly near thebottom of the feature. Example processing variables that should beproperly balanced against one another to ensure development of thesacrificial oxidant concentration differential include the concentrationof the sacrificial oxidant in bulk solution (e.g., where the sacrificialoxidant is H+, the pH of the electrolyte is important), the reductionpotential of the sacrificial oxidant, the reduction potentialexperienced during electroplating, the substrate rotation rate (and/orother factors affecting mass transfer within the electrolyte), etc. Invarious embodiments, the substrate may be rotated at a rate betweenabout 0-100 RPM, in some cases at least about 5 RPM, or at least about10 RPM.

Operation 708 describes that during plating, there should not be asubstantial concentration differential with respect to the metal ions inthe field region and near the top of the feature, compared to within thefeature, particularly near the feature bottom. In other words,deposition of the metal within the features should not be limited bymass transport of the metal ions. Otherwise, the metal could becomedepleted within the features, deleteriously affecting the desiredsuperconformal fill mechanism. Example processing variables that shouldbe properly balanced against one another to ensure that no substantialmetal concentration differential forms include the concentration ofmetal ions in solution, the reduction potential of the metal ions, thereduction potential experienced during electroplating, the substraterotation rate (and/or other factors affecting mass transfer within theelectrolyte), etc.

Because it is desired to establish a concentration differential withrespect to the sacrificial oxidant, but not with respect to the metalbeing plated, it is generally desirable to ensure that the metal ion isprovided to the electrolyte at a higher concentration than thesacrificial oxidant. In some cases, the concentration of the sacrificialoxidant may be at least about 10 times higher than the concentration ofthe metal ion in the bulk electrolyte.

In operation 709, a current efficiency differential develops between thefield region and within the substrate. In the field region, the currentefficiency remains low due to the abundance of sacrificial oxidantmolecules. As these sacrificial oxidant molecules are reduced, theydivert the reduction current away from the metal reduction reaction,leading to a relatively lower rate of metal deposition in the fieldregion and near the top of the feature. Within the feature, particularlynear the feature bottom, the current efficiency is initially low due tothe presence of the sacrificial oxidant molecules. However, due at leastin part to the high surface area to volume ratio within the features (aswell as the balance of all the various plating conditions), the currentefficiency near the feature bottom quickly rises during plating as thesacrificial oxidant molecules are depleted in this region, leading to arelatively high rate of metal deposition near the feature bottom. Asmentioned in operation 710, the differential current efficiency drivesthe superconformal fill mechanism, with metal deposition happeningrelatively faster near the bottom of the feature and relatively slowernear the top of the feature and in the field region. The result is thatthe feature fills from the bottom upwards, as shown in FIG. 2, forexample.

In a particular embodiment, the metal being deposited is cobalt, and thesacrificial oxidant is H⁺. Experimental results have shown that when thevarious processing conditions are properly balanced against one another(e.g., as described in relation to FIGS. 4-6), hydrogen ions work wellas sacrificial oxidant molecules in the context of superconformal cobaltfill. FIG. 8 describes the motivation behind selection of hydrogen ionsas the sacrificial oxidant in various embodiments. Specifically, FIG. 8shows a reductive wave of a cyclic voltammogram in electrolyte thatincludes Co²⁺ and H⁺ at various concentrations. In this system, H⁺ is anacceptable sacrificial oxidant at least partly because the magnitude ofthe reduction potential for H⁺ is lower than the magnitude of thereduction potential for Co²⁺, at least for certain electrolyte pHvalues. The results are especially promising for solutions having a pHof about 2, 3, or 4. At pH values of about 5 or greater, the hydrogenions are less abundant in the electrolyte, and the reduction potentialfor the hydrogen ions may be about equal to or greater than thereduction potential for the cobalt ions. As such, at these higher pHvalues, the superconformal fill mechanism is not likely to besuccessful.

In one example, an electrolyte for depositing cobalt may have thefollowing properties:

TABLE 1 Property Value Concentration of cobalt (II) salt/ 0.005-1Mcobalt (II) ions pH 2-4

Example cobalt (II) salts include, but are not limited to, cobalt (II)sulfate heptahydrate, cobalt (II) chloride hexahydrate, cobalt (II)nitrate, and combinations thereof. The cobalt salt is the source of thecobalt ions. In various embodiments, the cobalt ion concentration may bebetween about 10-100 mM, or between about 30-70 mM.

Example acids include, but are not limited to, boric acid, sulfuricacid, hydrochloric acid, phosphoric acid, and combinations thereof. Insome embodiments, boric acid may be provided at a concentration betweenabout 0.01-1 M, for example between about 0.05-0.6 M. Boric acid haspositive effects on cobalt nucleation (as well as nucleation of othermetals such as nickel), and is commonly used in various electroplatingapplications. The electrolyte may have a pH between about 2-4, forexample between about 3-4, with pH adjusted through the addition ofsulfuric acid, hydrochloric acid, phosphoric acid, or a combinationthereof. This may provide a hydrogen ion concentration between about0.1-10 mM, for example between about 0.1-1 mM. In cases where thesacrificial oxidant is a species other than hydrogen ions, theconcentration of the sacrificial oxidant may be between about 0.1-10 mM,for example between about 0.1-1 mM.

One example sacrificial oxidant is hydrogen ion, e.g., sourced fromsulfuric acid, hydrochloric acid, phosphoric acid, or other strong acid.Other example sacrificial oxidants include hydrogen peroxide, nitricacid, and dissolved oxygen.

In some embodiments where the electrolyte is prepared according to Table1, the electrolyte may be free or substantially free (e.g., containingonly trace amounts) of suppressor, accelerator, and leveler. In someother embodiments where electrolyte is prepared according to Table 2,one or more of these additives may be provided.

TABLE 2 Property Value Concentration of cobalt (II) salt/ 0.005-1Mcobalt (II) ions pH 2-4 Concentration of suppressor molecules 0-30 g/LConcentration of accelerator molecules 0-30 g/L Concentration of levelermolecules 0-30 g/L

In one example, referred to as Example 1, the cobalt ion concentrationmay be between about 10-100 mM, the boric acid concentration may bebetween about 0.05-0.6 mM, the pH of the electrolyte is between about2-4 (e.g., an H+ concentration between about 0.1-10 mM), the substrateis rotated at a rate between about 0-100 RPM, a 0-30 secondpre-conditioning step (e.g., as explained in relation to operation 703in FIG. 7) is provided after immersion and before application of anycurrent, and the substrate is plated at a constant current density atabout 4 mA/cm² or below (in various embodiments the constant currentdensity may be at least about 0.5 mA/cm² or at least about 1 mA/cm²).The cobalt ion concentration may be at least about 10 times higher thanthe concentration of hydrogen ion.

In another example, referred to as Example 2, the cobalt ionconcentration may be between about 10-100 mM, the boric acidconcentration may be between about 0.05-0.6 mM, the pH of theelectrolyte is between about 2-4 (e.g., an H+ concentration betweenabout 0.1-10 mM), the substrate is rotated at a rate between about 0-100RPM, a 0-30 second pre-conditioning step (e.g., as explained in relationto operation 703 in FIG. 7) is provided after immersion and beforeapplication of any current, and the substrate is plated with a rampingcurrent waveform that starts at a low current (e.g., as low as 0 mA/cm²)and ends at a higher current (e.g., as high as about 10 mA/cm²). Thecobalt ion concentration may be at least about 10 times higher than theconcentration of hydrogen ion.

In another example, referred to as Example 3, the conditions are asdescribed in relation to Example 1 or Example 2, except that theelectrolyte also includes a suppressor to enhance the superconformalfill mechanism. The suppressor may be provided at a concentration listedabove.

In another example, referred to as Example 4, the conditions are asdescribed in relation to any of Examples 1-3, except that an alternativesacrificial oxidant is provided. The concentration of the alternativesacrificial oxidant may be determined based on the properties of thesacrificial oxidant (e.g., using the methods described in relation toFIGS. 4-6). Example alternative sacrificial oxidant molecules havingsoluble reduction products include H2O2 and other peroxides, dissolvedO₂ and/or O₃, HNO₃, gluconic acid and other sugar acids, Fe(III), Cl₂,Br₂, and I₂.

In another example, referred to as Example 5, the electrolyte has acobalt ion concentration of about 50 mM, a boric acid concentration ofabout 0.5 M, and a pH of about 3. The electrolyte also has a suppressorpresent, e.g., functionalized PEG, PPG, etc. The substrate may berotated at a rate of about 50 RPM. After immersion and beforeapplication of current, a 1 second pre-conditioning step is appliedwhere no current is provided to the substrate. Current may be applied ina ramping waveform, starting at about 0 mA/cm² and rising to about 8mA/cm² over a period of about 60 seconds. The temperature of theelectrolyte may be about 25° C. This combination of conditions has beenshown to result in superconformal fill.

FIGS. 9A-9C depict experimental results showing a feature being filledusing the disclosed superconformal fill mechanism. The same depositionconditions were used to fill each of the features shown in FIGS. 9A-9C,except for deposition time. The deposition in FIG. 9A was stopped aftera short duration (after passing about 15 mC/cm² to the substrate), thedeposition in FIG. 9B was stopped after a longer duration (after passingabout 29 mC/cm² to the substrate), and the deposition in FIG. 9C wasstopped after the longest duration (after passing about 45 mC/cm² to thesubstrate). Therefore, when taken together, FIGS. 9A-9C illustrate arecessed feature being filled over time using the superconformal fillmechanism. As shown in FIGS. 9A and 9B, the metal is deposited in anearly flat profile, and the feature is filled from the bottom upwards.As shown in FIG. 9C, the resulting fill is very high quality, withoutany seams or voids. The deposition conditions used in relation to FIGS.9A-9C are those described in Example 5, above.

Apparatus

The methods described herein may be performed by any suitable apparatus.A suitable apparatus includes hardware for accomplishing the processoperations and a system controller having instructions for controllingprocess operations in accordance with the present embodiments. Forexample, in some embodiments, the hardware may include one or moreprocess stations included in a process tool.

FIG. 10 presents an example of an electroplating cell in whichelectroplating may occur. Often, an electroplating apparatus includesone or more electroplating cells in which the substrates (e.g., wafers)are processed. Only one electroplating cell is shown in FIG. 10 topreserve clarity. To optimize bottom-up electroplating, additives (e.g.,accelerators, suppressors, and levelers) are added to the electrolyte;however, an electrolyte with additives may react with the anode inundesirable ways. Therefore anodic and cathodic regions of the platingcell are sometimes separated by a membrane so that plating solutions ofdifferent composition may be used in each region. Plating solution inthe cathodic region is called catholyte; and in the anodic region,anolyte. A number of engineering designs can be used in order tointroduce anolyte and catholyte into the plating apparatus.

Referring to FIG. 10, a diagrammatical cross-sectional view of anelectroplating apparatus 1001 in accordance with one embodiment isshown. The plating bath 1003 contains the plating solution (having acomposition as provided herein), which is shown at a level 1005. Thecatholyte portion of this vessel is adapted for receiving substrates ina catholyte. A wafer 1007 is immersed into the plating solution and isheld by, e.g., a “clamshell” substrate holder 1009, mounted on arotatable spindle 1011, which allows rotation of clamshell substrateholder 1009 together with the wafer 1007. A general description of aclamshell-type plating apparatus having aspects suitable for use withthis invention is described in detail in U.S. Pat. No. 6,156,167 issuedto Patton et al., and U.S. Pat. No. 6,800,187 issued to Reid et al.,which are incorporated herein by reference in their entireties.

An anode 1013 is disposed below the wafer within the plating bath 1003and is separated from the wafer region by a membrane 1015, preferably anion selective membrane. For example, Nafion™ cationic exchange membrane(CEM) may be used. The region below the anodic membrane is oftenreferred to as an “anode chamber.” The ion-selective anode membrane 1015allows ionic communication between the anodic and cathodic regions ofthe plating cell, while preventing the particles generated at the anodefrom entering the proximity of the wafer and contaminating it. The anodemembrane is also useful in redistributing current flow during theplating process and thereby improving the plating uniformity. Detaileddescriptions of suitable anodic membranes are provided in U.S. Pat. Nos.6,126,798 and 6,569,299 issued to Reid et al., both incorporated hereinby reference in their entireties. Ion exchange membranes, such ascationic exchange membranes, are especially suitable for theseapplications. These membranes are typically made of ionomeric materials,such as perfluorinated co-polymers containing sulfonic groups (e.g.Nafion™), sulfonated polyimides, and other materials known to those ofskill in the art to be suitable for cation exchange. Selected examplesof suitable Nafion™ membranes include N324 and N424 membranes availablefrom Dupont de Nemours Co.

During plating the ions from the plating solution are deposited on thesubstrate. The metal ions must diffuse through the diffusion boundarylayer and into the TSV hole or other feature. A typical way to assistthe diffusion is through convection flow of the electroplating solutionprovided by the pump 1017. Additionally, a vibration agitation or sonicagitation member may be used as well as wafer rotation. For example, avibration transducer 1008 may be attached to the clamshell substrateholder 1009.

The plating solution is continuously provided to plating bath 1003 bythe pump 1017. Generally, the plating solution flows upwards through ananode membrane 1015 and a diffuser plate 1019 to the center of wafer1007 and then radially outward and across wafer 1007. The platingsolution also may be provided into the anodic region of the bath fromthe side of the plating bath 1003. The plating solution then overflowsplating bath 1003 to an overflow reservoir 1021. The plating solution isthen filtered (not shown) and returned to pump 1017 completing therecirculation of the plating solution. In certain configurations of theplating cell, a distinct electrolyte is circulated through the portionof the plating cell in which the anode is contained while mixing withthe main plating solution is prevented using sparingly permeablemembranes or ion selective membranes.

A reference electrode 1031 is located on the outside of the plating bath1003 in a separate chamber 1033, which chamber is replenished byoverflow from the main plating bath 1003. Alternatively, in someembodiments the reference electrode is positioned as close to thesubstrate surface as possible, and the reference electrode chamber isconnected via a capillary tube or by another method, to the side of thewafer substrate or directly under the wafer substrate. In some of thepreferred embodiments, the apparatus further includes contact senseleads that connect to the wafer periphery and which are configured tosense the potential of the metal seed layer at the periphery of thewafer but do not carry any current to the wafer.

A reference electrode 1031 is typically employed when electroplating ata controlled potential is desired. The reference electrode 1031 may beone of a variety of commonly used types such as mercury/mercury sulfate,silver chloride, saturated calomel, or copper metal. A contact senselead in direct contact with the wafer 1007 may be used in someembodiments, in addition to the reference electrode, for more accuratepotential measurement (not shown).

A DC power supply 1035 can be used to control current flow to the wafer1007. The power supply 1035 has a negative output lead 1039 electricallyconnected to wafer 1007 through one or more slip rings, brushes andcontacts (not shown). The positive output lead 1041 of power supply 1035is electrically connected to an anode 1013 located in plating bath 1003.The power supply 1035, a reference electrode 1031, and a contact senselead (not shown) can be connected to a system controller 1047, whichallows, among other functions, modulation of current and potentialprovided to the elements of electroplating cell. For example, thecontroller may allow electroplating in potential-controlled andcurrent-controlled regimes. The controller may include programinstructions specifying current and voltage levels that need to beapplied to various elements of the plating cell, as well as times atwhich these levels need to be changed. When forward current is applied,the power supply 1035 biases the wafer 1007 to have a negative potentialrelative to anode 1013. This causes an electrical current to flow fromanode 1013 to the wafer 1007, and an electrochemical reduction (e.g.Cu²⁺+2e⁻=Cu⁰) occurs on the wafer surface (the cathode), which resultsin the deposition of the electrically conductive layer (e.g. copper) onthe surfaces of the wafer. An inert anode 1014 may be installed belowthe wafer 1007 within the plating bath 1003 and separated from the waferregion by the membrane 1015.

The apparatus may also include a heater 1045 for maintaining thetemperature of the plating solution at a specific level. The platingsolution may be used to transfer the heat to the other elements of theplating bath. For example, when a wafer 1007 is loaded into the platingbath the heater 1045 and the pump 1017 may be turned on to circulate theplating solution through the electroplating apparatus 1001, until thetemperature throughout the apparatus becomes substantially uniform. Inone embodiment the heater is connected to the system controller 1047.The system controller 1047 may be connected to a thermocouple to receivefeedback of the plating solution temperature within the electroplatingapparatus and determine the need for additional heating.

The controller will typically include one or more memory devices and oneor more processors. The processor may include a CPU or computer, analogand/or digital input/output connections, stepper motor controllerboards, etc. In certain embodiments, the controller controls all of theactivities of the electroplating apparatus. Non-transitorymachine-readable media containing instructions for controlling processoperations in accordance with the present embodiments may be coupled tothe system controller.

Typically there will be a user interface associated with controller1047. The user interface may include a display screen, graphicalsoftware displays of the apparatus and/or process conditions, and userinput devices such as pointing devices, keyboards, touch screens,microphones, etc. The computer program code for controllingelectroplating processes can be written in any conventional computerreadable programming language: for example, assembly language, C, C++,Pascal, Fortran or others. Compiled object code or script is executed bythe processor to perform the tasks identified in the program. Oneexample of a plating apparatus that may be used according to theembodiments herein is the Lam Research Sabre tool. Electrodeposition canbe performed in components that form a larger electrodepositionapparatus.

FIG. 11 shows a schematic of a top view of an example electrodepositionapparatus. The electrodeposition apparatus 1100 can include threeseparate electroplating modules 1102, 1104, and 1106. Theelectrodeposition apparatus 1100 can also include three separate modules1112, 1114, and 1116 configured for various process operations. Forexample, in some embodiments, one or more of modules 1112, 1114, and1116 may be a spin rinse drying (SRD) module. In other embodiments, oneor more of the modules 1112, 1114, and 1116 may be post-electrofillmodules (PEMs), each configured to perform a function, such as edgebevel removal, backside etching, and acid cleaning of substrates afterthey have been processed by one of the electroplating modules 1102,1104, and 1106.

The electrodeposition apparatus 1100 includes a centralelectrodeposition chamber 1124. The central electrodeposition chamber1124 is a chamber that holds the chemical solution used as theelectroplating solution in the electroplating modules 1102, 1104, and1106. The electrodeposition apparatus 1100 also includes a dosing system1126 that may store and deliver additives for the electroplatingsolution. A chemical dilution module 1122 may store and mix chemicals tobe used as an etchant. A filtration and pumping unit 1128 may filter theelectroplating solution for the central electrodeposition chamber 1124and pump it to the electroplating modules.

A system controller 1130 provides electronic and interface controlsrequired to operate the electrodeposition apparatus 1100. The systemcontroller 1130 (which may include one or more physical or logicalcontrollers) controls some or all of the properties of theelectroplating apparatus 1100.

Signals for monitoring the process may be provided by analog and/ordigital input connections of the system controller 1130 from variousprocess tool sensors. The signals for controlling the process may beoutput on the analog and digital output connections of the process tool.Non-limiting examples of process tool sensors that may be monitoredinclude mass flow controllers, pressure sensors (such as manometers),thermocouples, optical position sensors, etc. Appropriately programmedfeedback and control algorithms may be used with data from these sensorsto maintain process conditions.

A hand-off tool 1140 may select a substrate from a substrate cassettesuch as the cassette 1142 or the cassette 1144. The cassettes 1142 or1144 may be front opening unified pods (FOUPs). A FOUP is an enclosuredesigned to hold substrates securely and safely in a controlledenvironment and to allow the substrates to be removed for processing ormeasurement by tools equipped with appropriate load ports and robotichandling systems. The hand-off tool 1140 may hold the substrate using avacuum attachment or some other attaching mechanism.

The hand-off tool 1140 may interface with a wafer handling station 1132,the cassettes 1142 or 1144, a transfer station 1150, or an aligner 1148.From the transfer station 1150, a hand-off tool 1146 may gain access tothe substrate. The transfer station 1150 may be a slot or a positionfrom and to which hand-off tools 1140 and 1146 may pass substrateswithout going through the aligner 1148. In some embodiments, however, toensure that a substrate is properly aligned on the hand-off tool 1146for precision delivery to an electroplating module, the hand-off tool1146 may align the substrate with an aligner 1148. The hand-off tool1146 may also deliver a substrate to one of the electroplating modules1102, 1104, or 1106 or to one of the three separate modules 1112, 1114,and 1116 configured for various process operations.

An example of a process operation according to the methods describedabove may proceed as follows: (1) electrodeposit copper or anothermaterial onto a substrate in the electroplating module 1104; (2) rinseand dry the substrate in SRD in module 1112; and, (3) perform edge bevelremoval in module 1114.

An apparatus configured to allow efficient cycling of substrates throughsequential plating, rinsing, drying, and PEM process operations may beuseful for implementations for use in a manufacturing environment. Toaccomplish this, the module 1112 can be configured as a spin rinse dryerand an edge bevel removal chamber. With such a module 1112, thesubstrate would only need to be transported between the electroplatingmodule 1104 and the module 1112 for the copper plating and EBRoperations. In some embodiments the methods described herein will beimplemented in a system which comprises an electroplating apparatus anda stepper.

An alternative embodiment of an electrodeposition apparatus 1200 isschematically illustrated in FIG. 12. In this embodiment, theelectrodeposition apparatus 1200 has a set of electroplating cells 1207,each containing an electroplating bath, in a paired or multiple “duet”configuration. In addition to electroplating per se, theelectrodeposition apparatus 1200 may perform a variety of otherelectroplating related processes and sub-steps, such as spin-rinsing,spin-drying, metal and silicon wet etching, electroless deposition,pre-wetting and pre-chemical treating, reducing, annealing, photoresiststripping, and surface pre-activation, for example. Theelectrodeposition apparatus 1200 is shown schematically looking top downin FIG. 12, and only a single level or “floor” is revealed in thefigure, but it is to be readily understood by one having ordinary skillin the art that such an apparatus, e.g., the Novellus Sabre™ 3 D tool,can have two or more levels “stacked” on top of each other, eachpotentially having identical or different types of processing stations.

Referring once again to FIG. 12, the substrates 1206 that are to beelectroplated are generally fed to the electrodeposition apparatus 1200through a front end loading FOUP 1201 and, in this example, are broughtfrom the FOUP to the main substrate processing area of theelectrodeposition apparatus 1200 via a front-end robot 1202 that canretract and move a substrate 1206 driven by a spindle 1203 in multipledimensions from one station to another of the accessible stations—twofront-end accessible stations 1204 and also two front-end accessiblestations 1208 are shown in this example. The front-end accessiblestations 1204 and 1208 may include, for example, pre-treatment stations,and spin rinse drying (SRD) stations. Lateral movement from side-to-sideof the front-end robot 1202 is accomplished utilizing robot track 1202a. Each of the substrates 1206 may be held by a cup/cone assembly (notshown) driven by a spindle 1203 connected to a motor (not shown), andthe motor may be attached to a mounting bracket 1209. Also shown in thisexample are the four “duets” of electroplating cells 1207, for a totalof eight electroplating cells 1207. A system controller (not shown) maybe coupled to the electrodeposition apparatus 1200 to control some orall of the properties of the electrodeposition apparatus 1200. Thesystem controller may be programmed or otherwise configured to executeinstructions according to processes described earlier herein.

System Controller

In some implementations, a controller is part of a system, which may bepart of the above-described examples. Such systems can comprisesemiconductor processing equipment, including a processing tool ortools, chamber or chambers, a platform or platforms for processing,and/or specific processing components (a wafer pedestal, a gas flowsystem, etc.). These systems may be integrated with electronics forcontrolling their operation before, during, and after processing of asemiconductor wafer or substrate. The electronics may be referred to asthe “controller,” which may control various components or subparts ofthe system or systems. The controller, depending on the processingrequirements and/or the type of system, may be programmed to control anyof the processes disclosed herein, including the delivery of processinggases, temperature settings (e.g., heating and/or cooling), pressuresettings, vacuum settings, power settings, radio frequency (RF)generator settings, RF matching circuit settings, frequency settings,flow rate settings, fluid delivery settings, positional and operationsettings, wafer transfers into and out of a tool and other transfertools and/or load locks connected to or interfaced with a specificsystem.

Broadly speaking, the controller may be defined as electronics havingvarious integrated circuits, logic, memory, and/or software that receiveinstructions, issue instructions, control operation, enable cleaningoperations, enable endpoint measurements, and the like. The integratedcircuits may include chips in the form of firmware that store programinstructions, digital signal processors (DSPs), chips defined asapplication specific integrated circuits (ASICs), and/or one or moremicroprocessors, or microcontrollers that execute program instructions(e.g., software). Program instructions may be instructions communicatedto the controller in the form of various individual settings (or programfiles), defining operational parameters for carrying out a particularprocess on or for a semiconductor wafer or to a system. The operationalparameters may, in some embodiments, be part of a recipe defined byprocess engineers to accomplish one or more processing steps during thefabrication of one or more layers, materials, metals, oxides, silicon,silicon dioxide, surfaces, circuits, and/or dies of a wafer.

The controller, in some implementations, may be a part of or coupled toa computer that is integrated with, coupled to the system, otherwisenetworked to the system, or a combination thereof. For example, thecontroller may be in the “cloud” or all or a part of a fab host computersystem, which can allow for remote access of the wafer processing. Thecomputer may enable remote access to the system to monitor currentprogress of fabrication operations, examine a history of pastfabrication operations, examine trends or performance metrics from aplurality of fabrication operations, to change parameters of currentprocessing, to set processing steps to follow a current processing, orto start a new process. In some examples, a remote computer (e.g. aserver) can provide process recipes to a system over a network, whichmay include a local network or the Internet. The remote computer mayinclude a user interface that enables entry or programming of parametersand/or settings, which are then communicated to the system from theremote computer. In some examples, the controller receives instructionsin the form of data, which specify parameters for each of the processingsteps to be performed during one or more operations. It should beunderstood that the parameters may be specific to the type of process tobe performed and the type of tool that the controller is configured tointerface with or control. Thus as described above, the controller maybe distributed, such as by comprising one or more discrete controllersthat are networked together and working towards a common purpose, suchas the processes and controls described herein. An example of adistributed controller for such purposes would be one or more integratedcircuits on a chamber in communication with one or more integratedcircuits located remotely (such as at the platform level or as part of aremote computer) that combine to control a process on the chamber.

Without limitation, example systems may include a plasma etch chamber ormodule, a deposition chamber or module, a spin-rinse chamber or module,a metal plating chamber or module, a clean chamber or module, a beveledge etch chamber or module, a physical vapor deposition (PVD) chamberor module, a chemical vapor deposition (CVD) chamber or module, anatomic layer deposition (ALD) chamber or module, an atomic layer etch(ALE) chamber or module, an ion implantation chamber or module, a trackchamber or module, and any other semiconductor processing systems thatmay be associated or used in the fabrication and/or manufacturing ofsemiconductor wafers.

As noted above, depending on the process step or steps to be performedby the tool, the controller might communicate with one or more of othertool circuits or modules, other tool components, cluster tools, othertool interfaces, adjacent tools, neighboring tools, tools locatedthroughout a factory, a main computer, another controller, or tools usedin material transport that bring containers of wafers to and from toollocations and/or load ports in a semiconductor manufacturing factory.

The various hardware and method embodiments described above may be usedin conjunction with lithographic patterning tools or processes, forexample, for the fabrication or manufacture of semiconductor devices,displays, LEDs, photovoltaic panels and the like. Typically, though notnecessarily, such tools/processes will be used or conducted together ina common fabrication facility.

Lithographic patterning of a film typically comprises some or all of thefollowing steps, each step enabled with a number of possible tools: (1)application of photoresist on a workpiece, e.g., a substrate having asilicon nitride film formed thereon, using a spin-on or spray-on tool;(2) curing of photoresist using a hot plate or furnace or other suitablecuring tool; (3) exposing the photoresist to visible or UV or x-raylight with a tool such as a wafer stepper; (4) developing the resist soas to selectively remove resist and thereby pattern it using a tool suchas a wet bench or a spray developer; (5) transferring the resist patterninto an underlying film or workpiece by using a dry or plasma-assistedetching tool; and (6) removing the resist using a tool such as an RF ormicrowave plasma resist stripper. In some embodiments, an ashable hardmask layer (such as an amorphous carbon layer) and another suitable hardmask (such as an antireflective layer) may be deposited prior toapplying the photoresist.

It is to be understood that the configurations and/or approachesdescribed herein are exemplary in nature, and that these specificembodiments or examples are not to be considered in a limiting sense,because numerous variations are possible. The specific routines ormethods described herein may represent one or more of any number ofprocessing strategies. As such, various acts illustrated may beperformed in the sequence illustrated, in other sequences, in parallel,or in some cases omitted. Likewise, the order of the above describedprocesses may be changed.

The subject matter of the present disclosure includes all novel andnonobvious combinations and sub-combinations of the various processes,systems and configurations, and other features, functions, acts, and/orproperties disclosed herein, as well as any and all equivalents thereof.

What is claimed is:
 1. A method of identifying a set of electroplatingconditions that will result in a superconformal fill mechanism, themethod comprising: (a) electroplating a first series of substrates in afirst test solution, wherein a rate of substrate rotation differsbetween different substrates in the first series of substrates, andwherein a current density differs between different substrates in thefirst series of substrates; (b) electroplating a second series ofsubstrates in a second test solution, wherein the rate of substraterotation differs between different substrates in the second series ofsubstrates, wherein the current density differs between differentsubstrates in the second series of substrates, and wherein the first andsecond test solutions have different concentrations of a sacrificialoxidant; (c) determining a current efficiency for each substrate in thefirst and second series of substrates; (d) analyzing the currentefficiency and the rate of substrate rotation for each substrate in thefirst and second series of substrates to identify electroplatingconditions, if any, where the current efficiency decreases as the rateof substrate rotation during deposition increases; (e) analyzing thecurrent efficiency and the concentration of sacrificial oxidant for eachsubstrate in the first and second series of substrates to identifyelectroplating conditions, if any, where the current efficiencydecreases as the concentration of sacrificial oxidant increases; (f)analyzing the current efficiency and the current density for eachsubstrate in the first and second series of substrates to identifyelectroplating conditions, if any, where the current efficiencyincreases as the current density increases; and (g) based on (d)-(f),identifying the set of electroplating conditions that will result in thesuperconformal fill mechanism, if any, where the set of electroplatingconditions that will result in the superconformal fill mechanism includeconditions where (i) the current efficiency decreases as the rate ofsubstrate rotation increases, (ii) the current efficiency decreases asthe concentration of sacrificial oxidant increases, and (iii) thecurrent efficiency increases as the current density increases.
 2. Themethod of claim 1, wherein the first and second test solutions comprisecobalt ions, and wherein a metal being deposited on the substrates inthe first and second series of substrates is cobalt.
 3. The method ofclaim 2, wherein the sacrificial oxidant is hydrogen ion.
 4. The methodof claim 1, wherein the sacrificial oxidant, or a material which acts asa source for the sacrificial oxidant, is selected from the groupconsisting of: a peroxide, dissolved O₂, dissolved O₃, HNO₃, a sugaracid, Cl₂, Br₂, and I₂, and combinations thereof.
 5. The method of claim1, wherein a metal being electroplated reduces at a first reductionpotential, wherein the sacrificial oxidant reduces at a secondpotential, and wherein for the set of electroplating conditions thatwill result in the superconformal fill mechanism, a magnitude of thefirst reduction potential is greater than a magnitude of the secondreduction potential.
 6. The method of claim 1, wherein the first andsecond test solutions are substantially free of suppressor, accelerator,and leveler.
 7. The method of claim 1, wherein the first and second testsolutions each comprise suppressor.
 8. The method of claim 1, whereinthe first and second test solutions each comprise cobalt and hydrogenions, wherein a concentration of cobalt ions in the first test solutionis at least about 10 times higher than a concentration of hydrogen ionsin the first test solution, and wherein a concentration of cobalt ionsin the second test solution is at least about 10 times higher than aconcentration of hydrogen ions in the second test solution.
 9. Themethod of claim 1, further comprising electroplating an additionalsubstrate using electroplating conditions that fall within the set ofelectroplating conditions that will result in the superconformal fillmechanism, wherein the additional substrate comprises a plurality ofrecessed features, and wherein the recessed features are filled usingthe superconformal fill mechanism.
 10. A method of electroplating arecessed feature on a substrate using a superconformal fill mechanism,the method comprising: (a) immersing the substrate in electrolyte, theelectrolyte comprising metal ions and a sacrificial oxidant; (b)applying current to the substrate to plate metal in the recessedfeature; (c) during (b), depleting a concentration of the sacrificialoxidant within the recessed feature to form a concentration differentialwith respect to the sacrificial oxidant, wherein the sacrificial oxidantbecomes relatively less abundant within the recessed feature andrelatively more abundant in a field region of the substrate; (d) during(b), developing a current efficiency differential, wherein the currentefficiency is relatively higher within the recessed feature andrelatively lower in the field region of the substrate; and (e) during(b), using the current efficiency differential to drive thesuperconformal fill mechanism that deposits metal relatively faster neara bottom of the recessed feature and relatively slower in the fieldregion of the substrate.
 11. The method of claim 10, wherein during (b),the metal ions are not mass transport limited, such that no substantialconcentration differential forms with respect to the metal ions.
 12. Themethod of claim 10, wherein the metal ions are cobalt ions and thesacrificial oxidant is hydrogen ions.
 13. The method of claim 12,wherein the electrolyte comprises about 10-100 mM cobalt ions, about0.05-0.6 M boric acid, a pH between about 2-4, and wherein aconcentration of cobalt ions in the electrolyte is at least about 10times higher than a concentration of hydrogen ions in the electrolyte.14. The method of claim 13, wherein during (b) the substrate is rotatedat a rate between about 1-100 RPM, and wherein during (b) current isapplied to the substrate at a constant current density of about 4 mA/cm²or below.
 15. The method of claim 14, further comprising after (a) andbefore (b), performing a pre-conditioning step where no current orpotential is applied to the substrate for a duration between about0.25-30 seconds.
 16. The method of claim 10, wherein the sacrificialoxidant, or a material that acts as a source for the sacrificialoxidant, is selected from the group consisting of: a peroxide, dissolvedO₂, dissolved O₃, HNO₃, a sugar acid, Cl₂, Br₂, and I₂, and combinationsthereof.
 17. The method of claim 10, wherein the electrolyte issubstantially free of suppressor, accelerator, and leveler.
 18. Themethod of claim 10, wherein the electrolyte further comprisessuppressor.
 19. The method of claim 10, wherein during (b) a currentdensity applied to the substrate increases from a starting currentdensity to an ending current density, the starting current density beingbetween about 0-4 mA/cm² and the ending current density being betweenabout 6-10 mA/cm².
 20. An apparatus for electroplating metal into arecessed feature using a superconformal fill mechanism, the apparatuscomprising: an electroplating chamber configured to hold electrolyte; asubstrate holder configured to immerse the substrate in the electrolyte;and a controller comprising executable instructions for: (a) immersingthe substrate in electrolyte, the electrolyte comprising metal ions anda sacrificial oxidant; (b) applying current to the substrate to platemetal in the recessed feature; (c) during (b), depleting a concentrationof the sacrificial oxidant within the recessed feature to form aconcentration differential with respect to the sacrificial oxidant,wherein the sacrificial oxidant becomes relatively less abundant withinthe recessed feature and relatively more abundant in a field region ofthe substrate; (d) during (b), developing a current efficiencydifferential, wherein the current efficiency is relatively higher withinthe recessed feature and relatively lower in the field region of thesubstrate; and (e) during (b), using the current efficiency differentialto drive the superconformal fill mechanism that deposits metalrelatively faster near a bottom of the recessed feature and relativelyslower in the field region of the substrate.